Pavement widener

ABSTRACT

A method and apparatus for depositing paving material in a widened course alongside an existing paved surface. Material deposited in a hopper of the apparatus is conveyed to one side and spread onto the course where a strikeoff blade levels the material to the desired width, grade and slope. A control circuit is provided to automatically control grade and slope in relation to predetermined reference datums. A grade sensor responsive to a first datum actuates the circuit to elevate or depress the inboard end of the blade for grade control, and a grade sensor responsive to a second datum actuates the circuit to elevate or depress the outboard end of the blade for slope control. In one form of the invention the second datum is the gravity force vector, and in another form this datum is the slope of the paved surface.

United States Patent Davin et al. [4 1 Jan. 25, 1972 1541 PAVEMENT WIDENER 3,216,337 11/1965 MacDonald ..94/44 [72] Inventors: Donald R. Davin, Sheibyville; Michael E. 3'264958 8/1966 Babb G Ch 1 3,292,511 l2/l966 Cheney... rant, al' eston, both Of Layton-u. [73 Assignee; BhwKnox c u- Equipment, Inc 3,466,989 9/1969 Ulrich ..94/44 Mattoon, ill. Primary Examiner-Nile C. Byers, Jr. [22] F'led: Sept 1969 AltorneyMandeville & Schweitzer [2]] Appl. No.: 860,584

[57] ABSTRACT 52 Us. 01. ..94/45 a, 94/46 AC A mum! and aPParatus lemming Paving a [51] IL CL i "Emc 19/22 widened course alongside an existing paved surface. Material [58] Field of Search ..94 45, 46, 39 44 delmsited a P is Side and spread onto the course where a strikeoff blade levels the [56] References cued material to the desired width, grade and slope. A control circuit is provided to automatically control grade and slope in UNITED STATES PATENTS relation to predetermined reference datums. A grade sensor responsive to a first datum actuates the circuit to elevate or irlunyon depress the inboard end of h blade f grade control and a l 1 l 1967 "94/46 grade sensor responsive to a second datum actuates the circuit 2'572776 5 9 "94/46 to elevate or depress the outboard end of the blade for slope 3 8 l Smith "94/44 control. in one form of the invention the second datum is the l 3 2 Hero 94/44 x gravity force vector, and in another form this datum is the I ll 63 "94/44 slope of the paved surface. 3,111,070 11/1963 Pollitz ..94/46 3,130,654 4/1964 Apel ..94/46 9 Claims, 7 Drawing Figures 4 11 a m O ll i: I J l PATENTED JANZS m2 SHEET 2 [IF 4 PATENTED JAN 25 1972 SHEET [1F 4 PAVEMENT WIDENER SUMMARY OF THE INVENTION This invention relates to paving machinery and more particularly relates to pavement wideners in which material is deposited in a course alongside a paved surface or the like, which may be a newly paved slab or a resurfaced slab.

Pavement wideners are used to deposit paving material along the shoulder of an existing paved surface. Construction of new pavement or the resurfacing of an older one will result in a dropofi' at the shoulder of considerable depth making it difficult to maneuver a dump truck or the like over the shoulder to spread the material. Conventional widening machinery thus rides on the existing pavement where it receives material from the truck and then moves the material to the side where a blade strikes off and levels it to the required width and grade. Conventional controls for such equipment may be of the joint matcher type which regulates elevation of the inner blade edge with respect to the existing pavement and thus controls grade only. It is desirable to additional control slope, and be able to vary this slope when entering curves or intersections. The present invention provides a method and apparatus for controlling both slope and grade in a pavement widener. With applicants invention it is possible to set a predetennined course both as to grade and slope and then selectively vary the slope, as desired, such as in a curve or at an intersection. Control of the slope operates as a slave to the grade control so that as grade varies, the preselected slope angle will be maintained throughout the course until changed by the operator.

The high cost of material used for widening has resulted in efforts to improve the efficiency of the widening operation. Slope control is one way to do this since material can be saved by maintaining a preselected constant slope. Applicants invention provides a widening machine which supplies this improved efficiency and savings in paving material.

It is an object of the invention to provide a method and apparatus for widening a pavement in which both grade and slope of the deposited material are automatically controlled by maintaining a predetermined blade position with respect to reference datums.

Another object is to provide a pavement-widening method in which paving material received by the widener is deposited to the side of the new course, a strikeoff blade moving with the widener levels and grades the material to a predetermined width, the vertical height of the inboard edge of the blade is elevated or depressed for grade control responsive to a grade datum, and the transverse slope of the blade is varied to maintain slope control responsive to a slope datum operating as a slave to grade control.

Another object is to provide an automatic grade and slope control system for a pavement widener having a sidewardly extending strikeoff blade in which the inboard edge of the blade is vertically adjusted responsive to sensing a grade datum, and in which the inboard edge of the blade is vertically adjusted for slope control responsive to transverse incline of the blade relative to a gravity datum.

Another object is to provide an automatic grade and slope control for a pavement widener in which the inboard edge of the blade is vertically adjusted for grade control responsive to a grade datum, and in which the outboard edge of the blade is vertically adjusted for slope control responsive to movement of a blade extension sidewardly projecting over a second grade datum at the opposite side of the existing pavement.

Another object is to provide an automatic grade and slope control for a pavement widener in which the inboard edge of the strikeoff blade is vertically adjusted to maintain a predetermined elevation with respect to a grade datum, in which the transverse slope of the blade is adjusted with respect to either a gravity datum to maintain a predetermined slope angle with respect to gravity, or to adjust blade slope responsive to a second grade datum at the opposite side of the pavement to maintain a preselected angle with respect to pavement slope.

These and other objects and advantages of the invention will become apparent when the following description is read in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view of a preferred form of a pavement widener incorporating features of the present invention;

FIG. 2 is a side elevation view of the widener of FIG. 1;

FIG. 3 is a schematic diagram illustrating a preferred control system for the invention;

FIG. 4 is an end elevation view of the widener illustrating one form of the control system;

FIG. 5 is an end elevation view of a modified widener incorporating another form of the control system;

FIG. 6 is an enlarged view of component elements of the invention taken along the line 6-6 of FIG. 1; and

FIG. 7 is an end elevation view of the elements of FIG. 6.

DETAILED DESCRIPTION Referring to the drawings and particularly FIGS. 1 and 2 a preferred form of the pavement widener is indicated generally at 10. Widener 10 comprises a self-propelled vehicle adapted to run over the existing road surface 12 and distribute paving material to either side, depending on blade positioning, down a widened course 14 abutting against the side of the pavement.

Typically the prepared undersurface 16 for the new course to be widened may be rough and undulating as it extends laterally from the pavement shoulder or dropoff resulting from either resurfacing of old pavement, new construction, or excavation alongside an existing road surface.

Widener 10 moves at a controlled speed to the right as viewed in FIGS. 1 and 2 and receives paving material from a dump truck, for example, which operates on road surface 12 and discharges into hopper 18 at the widener front end. The paving material may be of any type suitable for the particular application such as asphalt, rock aggregate, concrete, or dirt and the like. Two superposed courses can be run, such as a rock aggregate base as the first course followed by an overly ing asphalt course.

Widener 10 is powered by a suitable prime mover 20. mounted on the rear frame 22 for driving transmission 24 which in turn powers traction wheels 26, 28. A dual operator's station 30 at the forward end of the frame may be located on the right-hand side for better control and visibility while laying the course to the right. Station 30, including steering device 32 and operators seat 34, is adapted to be moved to the lefthand side for laying a course to the left. Operation of shift levers at the operators station is relayed to transmission 24 through shift tube 36.

Paving material received in hopper 18 is conveyed to either the right or left side by operation of conveyor 38. The conveyor comprises a suitable endless belt 40, preferably of an elastomer such as Neoprene, traveling on spaced rollers. The conveyor may be powered by conventional means such as a preferred infinitely variable-speed hydraulic drive, not shown, driven from prime mover 20. The conveyor may be mounted for transverse extension and retraction by suitable hydraulic actuators, not shown, which in conjunction with operator speed control of the belt provides complete control of paving material delivery to ensure that the proper amount of material is being delivered into the new course. Paving material moving from the end of the conveyor is guided onto the course by a pair of removable discharge aprons 42, 44 mounted on either side of the conveyor discharge end.

A strikeoff blade 46 is mounted on the side of the widener to level the deposited material into finished course 14 of predetermined width and controlled grade and slope. As illustrated in FIG. 2 blade 46 is contoured with a concave forward configuration to level and smooth the paving material over an irregular base, and push the excess material forwardly as the blade is moved along the course.

Blade 46 is mounted at its front end on widener frame 22 by support assembly 48 adapted to vertically adjust the inboard end of the blade for automatic grade control, as will presently be described. The outboard end of the blade overhangs the new course and is supported from the widener frame by a telescoping beam assembly 50 comprising an outer beam 52 pivotally secured at 54 to the blade and telescoping within inner beam 56. The inner beam is pivotally mounted at 58 to the lower end of post 60 on frame 22 to swivel about a vertical axis. This affords selective adjustment of the course width. The telescoping members of beam assembly 50 can be unlocked and swung about post 60 until the outboard end of blade 46 is in the position desired. The beam members 52, 56 are then locked together by suitable means such as a locking pin, not shown. Forward tilt or rake of blade 46 can be adjusted by suitable means such as outer support arm 62 mounted between beam 52 and the upper edge of blade 46. Ann 62 may comprise a turnbuckle assembly for selective adjustment of blade tilt.

Vertical adjustment of the outer end of blade 46 is efiected through operation of slope control cylinder 64 secured at its upper end to post 60 and at its lower end to inner beam 56. Extension and retraction of cylinder 64 will respectively lower and raise the blade end in accordance with operation of the control circuit as explained hereafter.

Although the blade is illustrated as mounted on the righthand side of widener the present invention affords an alternative left-hand mounting. For this purpose a strikeoff support assembly 66 and rear support post 68 are provided on the opposite side of frame 22. For mounting the blade to the left, it is only necessary to release the blade and beam 50 from frame 22 without releasing the connection 54, turn both the blade and beam over, and reassemble to support 66 and post 68 on the opposite side with slope control cylinder 64 installed above the new blade position.

An inner cutoff plate 70 is mounted at 72 to the inboard blade end. Similarly an outer edger plate 74 is pivotally mounted at 76 to the outboard end of the blade and is supported in a forward direction by adjustable turnbuckle 78. Both cutoff plate 70 and edger plate 74 confine the material to the desired width of the course and, when the course width is changed by adjusting the length of beam 50, the angle of edger plate 74 would be correspondingly adjusted to maintain a straight outer course edge. During width changeover inner cutoff plates 70 remains in the position illustrated relative to the Widener.

Details of the preferred mounting arrangement for the blade are illustrated in FIGS. 4, 6 and 7. Support assembly 48 for the inboard edge of the blade comprises an extensible hydraulic cylinder 80 mounted at its lower end to support column 84, which is secured to frame 22, and at its upper end to inner support 82 which is slidable mounted within support column 84. The lower end of the support 82 is in turn pivotally mounted to the inboard edge of blade 46 through a suitable pin connection at 86 (FIG. 2). A vertical slot or guideway 88 is formed in the side of support column 84 to slidably receive the pin connection 86. A support arm 90 secured at one end to inner cutoff plate 70 and at its other end to inner support 82 moves through a vertical slot 92 in the support column so that the eutoff plate will move vertically upon adjustment of the blade.

While the means for vertically adjusting both the inboard and outboard edges of the blade has been shown as hydraulic cylinders 80 and 64 it is understood that other types of actuators can be provided, as for example, electric motors and the like.

Automatic control of blade 46 with respect to predetermined grade and slope references is effected through operation of the preferred control circuit illustrated generally at 94 in FIG. 3. Control circuit 94 operates to vertically adjust the inboard edge of blade 46 for grade control and the outboard edge for slope control. Grade control is the adjustment of blade height as a function of a predetermined datum plane or line extending in the direction of travel of the Widener. The datum for grade control preferably is the surface of the inner edge of existing pavement 12 although it could be a straight wire or the like stretched along the path of travel and defining the desired grade to be followed. Slope control is the adjustment of transverse blade angle with respect to a slope datum which follows with, or is a slave of, grade adjustment. in the embodiment illustrated in FIG. 4 the vertical force vector of gravity is used as the slope datum, while in the embodiment of FIG. 5 the transverse slope of existing pavement 12 is used as this datum. In a typical operation for either modification the operator would initially select the desired blade slope with respect to the datum being used, maintain this slope automatically via the control system of the invention throughout a course such as a straight run, and then vary the slope when running a course through a curve or at a road intersection, for example. Control system 94 maintains both grade and slope control with a high degree of accuracy so that the resulting widened course 14 can be laid down faster, with less paving material, and with greater efficiency.

Control circuit 94 is used in the embodiment of FIG. 4 and comprises grade control cylinder operating under influence of control fluid received from electrically operated solenoid valve 96, and slope control cylinder 64 operating under influence of fluid received from electrically operated solenoid valve 98.

Both solenoid valves 96 and 98 are operated responsive to signals received from respective electrical control circuits 116, 142 which in turn receive adjusting control signals from grade sensor 102 and slope sensor 104.

Grade sensor 102 is conventional and, as illustrated in FIGS. 6 and 7, is mounted for vertical movement with inner support 82 by means of rearwardly extending arm 103, depending arm 105, and bracket 107. The height of the sensor relative to road surface can be adjusted by operation of lock device 109 connecting arm 103 to arm 105.

A wand 106 is pivotally mounted at 108 to the grade sensor and when rotated from its null position operates to direct an electrical signal through conductors 110, 1 12 into circuit 1 16. A shoe 114 is pivotally mounted at the lower end of the wand for sliding engagement with the grade datum such as pavement surface 12. It is preferred to adjust sensor 102 so that the null position of wand 106 is at the illustrated 45 trailing position with respect to the sensor at which no electrical signal is produced. As the wand moves closer to the reference surface it would assume a position as at 106"; and conversely when moved away from the surface it would assume a position as at 106". Grade sensor 102 produces a control signal responsive to rotation of the wand in either direction from the 45 position, and preferably this may comprise a conventional potentiometric type sensing device in a wheatstone bridge circuit. A change in resistance of the bridge produces a voltage in the circuit which is the signal that is maintained until the null point is again reached. Alternatively, rotation of the wand may operate to open and close electrical contacts, with a separate set of contacts provided for rotation in either direction from the 45 position. These contracts may be in the form of limit switches.

Grade sensor 102 also incorporates conventional means, not shown, to adjust the amount of angular deviation of wand 106 which will unbalance the bridge circuit. Where the alternative electrical contacts are utilized this adjusting means would vary the angular deviation required to close the contacts.

Control signals received from sensor 102 are amplified by circuit 116 and directed through conductors 118, 120 to operate solenoid valve 96 in the direction required to actuate cylinder 80 for cancelling the control signal. Thus, if wand 106 moves upwardly to the position at 106', control circuit 94 actuates cylinder 80 to raise the strikeoff blade and thus raise sensor 102 until the wand returns to its 45 position. Cylinder 80 is actuated by hydraulic fluid received from pump 122 directed through flow divider 124, valve 96, and a selected one of conduits 126, 128 witlfreturn fluid flowing through the other of the conduits through valve 96, conduit 130, valve 98, and to reservoir 132.

A restrictor 13, preferably an orifice, may be provided in conduit 123 to limit flow therethrough when a down signal is received to move the blade downwardly. Restrictor 134 reduces overtravel of the stril'eoff blade which otherwise could occur as a result of the weight of the cylinder acting as a pump during downward movement.

Slope control cylinder 64 extends and retracts to elevate or depress the outboard end of the blade responsive to slope sensor 104. Slope sensor 104 is mounted on the rearward side of blade 46 intermediate the ends thereof and senses the transverse slope of the blade with respect to the vertical, as determined by the force vector of gravity. A weighted pendulum 136 mounted within the sensor varies its position with respect to the blade as the transverse inclination of the blade varies. This change in pendulum position is preferably sensed by a wiper which swings across the winding of a conventional wheatstone bridge circuit. When the pendulum swings past the null point of the bridge a signal directed through conductors I38, 140 is amplified in circuit 142 and directed through conductors 144, 146 to actuate solenoid valve 98. Fluid under pressure in hydraulic conduit 130 is then directed into a selected one of the conduits 148, 150 to actuate cylinder 64, with return fluid directed through the other conduit back to reservoir 132. The cylinder is actuated in the direction required to cancel the signal in circuit 142. A restrictor or orifice 152 may be provided in conduit 150 to reduce overtravel effect of a down signal in a manner similar to that explained for actuator 31).

Conventional means, not shown, are provided to selectively adjust the blade slope position at which slope sensor MM is in its null position. This determines a transverse angle of the blade which will be maintained with respect to the force vector of gravity throughout a widening operation. Because the vertical position of the inboard edge of blade 146 is determined solely by the grade reference datum, slope sensor lll l will operate as a slave to the grade sensor and maintain the preselected transverse blade slope throughout changes in grade.

in operation of the embodiment of FIG. 4 the control circuit is first adjusted to set the null positions of the sensors with the blade in the desired elevation and slope along the course. This is done by first raising the inboard end of blade 46 to the desired vertical relationship to the edge of the road surface, and then adjusting grade sensor 102 so that wand 106 is at a 45 trailing position with no control signal being produced. Grade control circuit 116 will now maintain the inboard edge of the blade at this preset elevation with respect to the road surface datum through control of cylinder 80. The outboard end of the blade is set up in the desired slope after the inboard end is in position. Slope sensor 104 is then adjusted to its null position with no control signal being produced. The sensor will continue to maintain this strikeoff angle with respect to the vertical through control of cylinder 64.

In the modification of FIG. 5 strikeoff blade slope is automatically controlled by an outer grade sensor i154 mounted on a beam or feedback arm 156 which is rigidly mounted to blade 46 and extends transversely under the Widener.

Arm 156 is mounted to the blade about transverse pivot point 157 located at the inner edge of the blade and thus vertically movable therewith.

Sensor 154 may be of similar construction to that of inner grade sensor 02 with a suitable wand or sensing element 158 moving in contact with the outer grade reference, such as the road surface or suitable guide wire. The control circuit for this embodiment preferably is similar to control circuit 94 of FIG. 3, but with grade sensor 154 replacing gravity sensor 194. Suitable means may be provided to adjust the null position of sensor 154 at which no control signal is proguged. Vertical movement of sensor 154 with respect to the outer road surface operates wand 158 from its nulLposition to produce control signals for actuating cylinder 6-5. Eylinds: '34 their adjusts the outer elevation of blade $6 in a direction to cancel the control signals and thereby maintain a preselected blade slope angle with respect to the slope of a plane defined by the outer and inner edges of pavement 12, which thus becomes the reference datum for blade slope control. Because arm I56 and sensor 154 move with the inner edge of blade 46, sensor 154 thus is a slave to sensor 102 so that the transverse slope of blade 46 will be maintained at a predetermined angle with respect to the slope of pavement 12 throughout grade change along the course.

In operation of the embodiment of FIG. 5 the inboard end of the strikeoff blade is first adjusted to the desired vertical clearance with respect to the inner edge of the road surface. Grade sensor 102 is then adjusted to its null position. The transverse slope of blade 46 is then adjusted to the desired angle with respect to the slope of road surface 12, and outer sensor 154 is adjusted to its null position. This blade slope angle will then be maintained throughout the course or until the operator may desire to readjust the null position of sensor 154 to alter the blade slope, such as when entering a curve or at an intersection.

It will be understood that various changes in the details, steps and arrangement of parts, which have been described and illustrated to explain the nature of invention, may be made by those skilled in the art within the principle and scope of the invention.

What is claimed is:

l. A pavement-widening apparatus for depositing paving material in a course alongside an existing paved surface including the combination of: a tractor adapted for movement along the paved surface; means on the tractor to receive paving materials and direct the same for deposit into said course; strikeoff blade means mounted on the tractor and extending transversely over said course to level the paving material; grade control means associated with said tractor and said strikeoff blade means to automatically adjust the elevation of the inner edge of the blade means for maintaining a predetermined elevation with respect to a given grade datum; said grade control means including a grade-sensing element positioned closely adjacent to the inner edge of said blade and actuator means for positively adjusting the position of said inner edge in response to said sensing element; and, slope control means associated with said tractor and said strikeoff blade means to automatically adjust the lateral slope of the blade means for maintaining a predetermined blade slope with respect to a given slope datum.

2. The apparatus of claim 1 wherein the blade means comprises a lateral and rearwardly extending blade, means including said actuator means associated with said tractor and said blade to mount the blade at its forward end on the tractor for vertical grade control movement; and means associated with said tractor and blade to mount the blade at its rearward end on the tractor for vertical slope control movement; said grade control means being operative to produce grade control signals responsive to vertical movement of the blade forward edge above and below the given grade datum, said actuator means being associated with said tractor and blade to raise and lower the blade forward edge in a direction to cancel the grade control signals, said slope control means including slope sensing means to produce slope control signals responsive to transverse angular deflection of the blade from the given slope datum, and including means to raise and lower the blade rearward edge in a direction to cancel the slope signals and maintain the given blade slope.

3. The apparatus of claim 2 wherein the grade datum comprises the pavement surface adjacent the widened course, and the grade-sensing means includes a sensing element in moving contact with said pavement surface closely adjacent the forward edge of the blade, said element having a null position relative to said surface and said blade forward edge producing no control signal when a preselected blade forward edge elevation relative to said surface is attained, the grade-sensing means operating to produce said grade control signals when said element is moved from said null position responsive to vertical movement of said blade forward edge above or below said predetermined position.

4. The apparatus of claim 2 wherein said slope datum is the force vector of gravity, and said slope-sensing means comprises a gravity-sensing element mounted on said blade and having a null position producing no control signals when the blade slope is at a predetermined angular position with respect to said element, the slope-sensing means operating to produce said slope control signals responsive to relative angular deflection of the element from said predetermined angular position.

5. The apparatus of claim 4 and further including means to adjust the null position of said element with respect to grade slope at which no signals are produced for selectively varying said predetermined blade slope along different portions of said course.

6. The apparatus of claim 2 wherein said slope datum comprises the transverse slope of the existing pavement, and said slope-sensing means comprises means producing said slope control signals responsive to transverse angular deflection of said blade from a given angular position with respect to said pavement slope.

7. The apparatus of claim 6 wherein said slope-sensing means further comprises means sensing a second grade datum longitudinally extending along the existing pavement at a locus spaced outwardly from the first-mentioned grade datum,

and arm means to mount the slope-sensing means for vertical movement with said blade and for pivotal movement with said blade above a longitudinal axis defined by the pivotal connection between the blade and tractor.

8. The apparatus of claim 7 wherein said slope-sensing means includes an element in moving contact with said second grade datum, said element having a null position in which no slope control signals are produced when said first and second grade datums locate a plane with respect to which the blade defines said given angular position; the slope-sensing means operating to produce said slope control signals responsive to movement of said element sensing a change in elevation between said first and second grade datums, said slope signals operating to vertically adjust the outer edge of said blade and move said arm means about said pivotal connection to cancel the signals and maintain said predetermined angular position of the blade.

9. The apparatus of claim 8 and further including means to selectively adjust the null position of said element to selectively vary the angular position between the blade and pavement slope throughout different portions of said course. 

1. A pavement-widening apparatus for depositing paving material in a course alongside an existing paved surface including the combination of: a tractor adapted for movement along the paved surface; means on the tractor to receive paving materials and direct the same for deposit into said course; strikeoff blade means mounted on the tractor and extending transversely over said course to level the paving material; grade control means associated with said tractor and said strikeoff blade means to automatically adjust the elevation of the inner edge of the blade means for maintaining a predetermined elevation with respect to a given grade datum; said grade control means including a gradesensing element positioned closely adjacent to the inner edge of said blade and actuator means for positively adjusting the position of said inner edge in response to said sensing element; and, slope control means associated with said tractor and said strikeoff blade means to automatically adjust the lateral slope of the blade means for maintaining a predetermined blade slope with respect to a given slope datum.
 2. The apparatus of claim 1 wherein the blade means comprises a lateral and rearwardly extending blade, means including said actuator means associated with said tractor and said blade to mount the blade at its forward end on the tractor for vertical grade control movement; and means associated with said tractor and blade to mount the blade at its rearward end on the tractor for vertical slope control movement; said grade control means being operative to produce grade control signals responsive to vertical movement of the blade forward edge above and below the given grade datum, said actuator means being associated with said tractor and blade to raise and lower the blade forward edge in a direction to cancel the grade control signals, said slope control means including slope sensing means to produce slope control signals responsive to transverse angular deflection of the blade from the given slope datum, and including means to raise and lower the blade rearward edge in a direction to cancel the slope signals and maintain the given blade slope.
 3. The apparatus of claim 2 wherein the grade datum comprises the pavement surface adjacent the widened course, and the grade-sensing means includes a sensing element in moving contact with said pavement surface closely adjacent the forward edge of the blade, said element having a null position relative to said surface and said blade forward edge producing no control signal when a preselected blade forward edge elevation relative to said surface is attained, the grade-sensing means operating to produce said grade control signals when said element is moved from said null position responsive to vertical movement of said blade forward edge above or below said predetermined position.
 4. The apparatus of claim 2 wherein said slope datum is the force vector of gravity, and said slope-sensing means comprises a gravity-sensing element mounted on said blade and having a null position producing no control signals when the blade slope is at a predetermined angular position with respect to said element, the slope-sensing means operating to produce said slope control signals responsive to relative angular deflection of the element from said predetermined angular position.
 5. The apparatus of claim 4 and further including means to adjust the null position of said element with respect to grade slope at which no signals are produced for selectively varying said predetermined blade slope along different portions of said course.
 6. The apparatus of claim 2 wherein said slope datum comprises the transverse slope of the existing pavement, and said slope-sensing means comprises means producing said slope control signals responsive to transverse angular deflection of said blade from a given angular position with respect to said pavement slope.
 7. The apparatus of claim 6 wherein said slope-sensing means further comprises means sensing a sEcond grade datum longitudinally extending along the existing pavement at a locus spaced outwardly from the first-mentioned grade datum, and arm means to mount the slope-sensing means for vertical movement with said blade and for pivotal movement with said blade above a longitudinal axis defined by the pivotal connection between the blade and tractor.
 8. The apparatus of claim 7 wherein said slope-sensing means includes an element in moving contact with said second grade datum, said element having a null position in which no slope control signals are produced when said first and second grade datums locate a plane with respect to which the blade defines said given angular position; the slope-sensing means operating to produce said slope control signals responsive to movement of said element sensing a change in elevation between said first and second grade datums, said slope signals operating to vertically adjust the outer edge of said blade and move said arm means about said pivotal connection to cancel the signals and maintain said predetermined angular position of the blade.
 9. The apparatus of claim 8 and further including means to selectively adjust the null position of said element to selectively vary the angular position between the blade and pavement slope throughout different portions of said course. 